Enhanced hydrogen sorption kinetics of MgH₂ catalyzed by a novel layered Ni/Al₂O₃ hybrid

Metal-containing catalysts have been successfully applied in the Mg-based hydrogen storage materials. Here, a layered Ni/Al₂O₃ obtained by calcination of NiAl-layered double hydroxide (NiAl-LDH) is firstly reported for enhancing hydrogen sorption kinetics of MgH₂. The hybrid catalyst of Ni/Al₂O₃ with high stability shows better catalytic performance than the corresponding complex oxides: the onset dehydrogenation temperature of MgH₂-Ni/Al₂O₃ (190 °C) is much lower than that of MgH₂-NiO/Al₂O₃ (240 °C) and the as-milled MgH₂ (298 °C), and the MgH₂-5 wt% Ni/Al₂O₃ desorbs about 5.6 wt% hydrogen within 3500 s at 275 °C, while only 4.6 wt% hydrogen is released for MgH₂-5 wt% NiO/Al₂O₃ and the undoped MgH₂ can hardly dehydrogenate at the same conditions. The catalytic mechanism of Ni/Al₂O₃ was investigated in detail by combining the experiment and density functional theory (DFT) calculations. The enhanced hydrogen desorption kinetics is mainly due to the destabilizing effect of MgH₂ caused by Ni/Al₂O₃ acting as electron acceptors to capture the electrons in the Mg−H bond, resulting in a weakening of the bond strength. This study might be of interest for designing high-efficiency metal-metal oxide hybrid catalysts applied in the field of hydrogen storage.